Cellular telephone fraud is a major problem faced by every cellular service provider today. One popular fraud scheme is called "cloning." A pirate monitors a control channel of the cellular telephone network, and during a call set-up process of an authorized cellular telephone, obtains its electronic serial number (ESN) and mobile identification number (MIN) which are transmitted over the control channel. The pirate then programs the ESN and MIN into another cellular telephone for illegal access to the cellular telephone network.
One current solution to the cloning fraud problem has been to require a separate personal identification number (PIN) during a call set-up process. While use of the PIN is inconvenient for a valid subscriber, it does makes access to the cellular telephone network more difficult. Another solution to cloning is to use an electronic fingerprint identification technique which is expected to be widely used in the near future. With the recent advent of these solutions to cloning fraud, it is anticipated that the pirates will try to find other methods to gain illegal access to the cellular telephone network.
One potential method recognized by the applicants is that a pirate may be able to simply "grab" or steal an active voice channel that is already being used by a valid subscriber. Either due to proximity to the cell site or relatively high power output, the pirate's cellular telephone can grab the voice channel simply by transmitting on the same voice channel. Then a well-known feature such as call conferencing is used to gain access to the cellular telephone network. Using the call conferencing feature, the pirate can now place a call to anywhere in the world. This channel grabbing method completely bypasses the call set-up process that occurs on the control channel and offers the pirate more anonymity and flexibility than the cloning fraud scheme. Moreover, only minor modification to most standard cellular telephones is necessary to convert any telephone into an unauthorized channel grabbing cellular telephone. Thus, the channel grabbing technique may provide pirates with an attractive alternative to cloning fraud. The applicants anticipate a large number of pirates will start using the new technique in the near future.
Therefore, it can be appreciated that there is a significant need for a method and system for detecting channel grabbing in a cellular telephone network. Once channel grabbing is detected, there is also a need to provide a technique to prevent the channel grabber from placing a telephone call. The present invention provides these and other advantages as will be illustrated by the following description and accompanying figures.